Endogenous Bone Marrow-Derived Stem Cell Mobilization and Homing for In Situ Tissue Regeneration.

In mammals, post-injury repair and regenerative events rely predominantly on stem cell function. Stem cell transplantation has achieved considerable success in animals but remains unfavorable for humans because of the unavoidable drawbacks. Nevertheless, substantial evidence suggests the regenerative potential of endogenous stem cells can be improved for functional and structural recovery of tissue damage or in disease conditions. Endogenous stem cells are mostly quiescent under steady-state conditions and reside in their niche. Once faced with tissue injury, physiological and molecular changes within the niche or from distant tissues activate the migration, proliferation, and differentiation of stem cells, contributing to tissue repair. Tissue regeneration is augmented by artificially amplifying the factors that promote stem cell mobilization or enhance the homing of endogenous stem cells. This cell-free strategy, known as "in situ tissue regeneration," represents a safer and more efficient means to conduct tissue regeneration. Bone marrow (BM) is considered the central niche and main reservoir of many types of stem cells. These stem cells hold great therapeutic potential for the regeneration of multiple injured tissues. Herein, we review recent strategies for promoting in situ tissue regeneration through BM-derived stem cell mobilization or homing in animal models as well as in human trials. With the advancement in biomaterial engineering, chemoattractant signals combined with functionalized bioscaffolds have accomplished sustained activation of endogenous BM-derived stem cells that can be used as an attractive strategy for efficient in situ tissue regeneration.

Migrasomes from adipose derived stem cells enrich CXCL12 to recruit stem cells via CXCR4/RhoA for a positive feedback loop mediating soft tissue regeneration.

BACKGROUND: Adipose-derived stem cells (ASCs) represent the most advantageous choice for soft tissue regeneration. Studies proved the recruitment of ASCs post tissue injury was mediated by chemokine CXCL12, but the mechanism by which CXCL12 is generated after tissue injury remains unclear. Migrasomes are newly discovered membrane-bound organelles that could deliver CXCL12 spatially and temporally in vivo. In this study, we sought to investigate whether migrasomes participate ASC-mediated tissue regeneration. METHODS: Discrepant and asymmetrical soft tissue regeneration mice model were established, in which HE staining, immunofluorescent staining, western blot and qPCR were conducted to confirm the role of CXCL12 and migrasomes in ASC-mediated tissue regeneration. Characterization of ASC-derived migrasomes were carried out by confocal microscopy, scanning electron microscopy, transmission electron microscopy as well as western blot analysis. The function and mechanism of migrasomes were further testified by assisting tissue regeneration with isolated migrasomes in vivo and by in vitro transwell combined with co-culture system. RESULTS: Here, we show for the first time that migrasomes participate in soft tissue regeneration. ASCs generate migrasomes enriched with CXCL12 to mediate tissue regeneration. Migrasomes from ASCs could promote stem cells migration by activating CXCR4/RhoA signaling in vivo and in vitro. Chemoattracted ASCs facilitate regeneration, as demonstrated by the upregulation of an adipogenesis-associated protein. This positive feed-back-loop creates a favorable microenvironment for soft tissue regeneration. Thus, migrasomes represent a new therapeutic target for ASC-mediated tissue regeneration. CONCLUSIONS: Our findings reveal a previously unknown function of ASCs in mediating tissue regeneration by generating migrasomes. The ASC-derived migrasomes can restore tissue regeneration by recruiting stem cells, which highlighting the potential application of ASC-derived migrasomes in regenerative medicine.

Lymphatic Vessel-Mediated Attenuation of Persistent Macrophage Infiltration Improves Fat Grafting Outcomes in Mice Models.

BACKGROUND: Persistent macrophage infiltration may lead to adverse consequences, such as calcifications and nodules in fat grafts. Lymphatic vessels, which transport inflammatory cells, are involved in regulating inflammatory responses. Less is known, however, about lymphatic vessels after fat grafting. OBJECTIVES: The aim of this study was to explore the regulation of fat graft survival by lymphatic vessels. METHODS: A common adipose graft model was constructed to assess the processes responsible for changes in the number of lymphatic vessels in grafts. Adipose tissue samples from C57/BL6 mice and green fluorescent protein-expressing mice were cross-grafted to determine the source of lymphatic vessels. The number of lymphatic vessels in the grafts was increased by treatment with vascular endothelial growth factor C, and the effects of this increase on fat grafting were evaluated. RESULTS: The number of lymphatic vessels was greater in postgrafted fat than in inguinal fat before transplantation, with lymphatic vessels in these grafts gradually transitioning from donor to recipient sources. Lymphatic vessels grew more slowly than blood vessels during early stages of grafting; during later stages, however, the number of blood vessels declined markedly, with more lymphatic vessels than blood vessels being observed 60 days after grafting. Vascular endothelial growth factor C treatment increased graft lymphatics and distant volume retention, while reducing fibrosis and oil sacs. Lymphatic vessels acted as drainage channels for macrophages, with the degree of sustained macrophage infiltration decreasing with increases in the number of lymphatic vessels. CONCLUSIONS: Increasing the number of lymphatic vessels is beneficial for fat graft survival, which may be related to a reduction in prolonged macrophage infiltration.

Ultra-condensed Fat: A Novel Fat Product for Volume Augmentation.

BACKGROUND: Fat transplantation retention rate is individualized and unpredictable. The presence of blood components and oil droplets in the injected lipoaspirate increases inflammation and fibrosis in a dose-dependent manner, and is probably the key factor associated with poor retention. OBJECTIVES: This study describes a volumetric fat grafting strategy based on optimization of grafts via screening intact fat particles and absorbing free oil droplets and impurities. METHODS: Centrifuged fat components were analyzed by n-hexane leaching. A special device was applied to de-oil intact fat components and obtain ultra-condensed fat (UCF). UCF was evaluated by scanning electron microscopy, particle size analysis, and flow cytometric analysis. Histological and immunohistochemical changes were investigated in a nude mouse fat graft model over 90 days. RESULTS: The lower 50% of centrifuged fat was concentrated to 40% of the original volume to obtain UCF. In UCF, the free oil droplet content was less than 10%, more than 80% of particles were larger than 1000 µm, and architecturally important fat components were present. The retention rate of UCF was significantly higher than that of Coleman fat on day 90 (57.5 ± 2.7% vs. 32.8 ± 2.5%, p < 0.001). Histological analysis detected small preadipocytes with multiple intracellular lipid droplets on day 3 in UCF grafts, indicative of early adipogenesis. Angiogenesis and macrophage infiltration were observed in UCF grafts soon after transplantation. CONCLUSION: Adipose regeneration with UCF involves rapid macrophage infiltration and exit, resulting in angiogenesis and adipogenesis. UCF may serve as a lipofiller which is beneficial for fat regeneration. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors http://www.springer.com/00266 .

Alternatively activated macrophages at the recipient site improve fat graft retention by promoting angiogenesis and adipogenesis.

The inflammatory response mediated by macrophages plays a role in tissue repair. Macrophages preferentially infiltrate the donor site and subsequently, infiltrate the recipient site after fat grafting. This study aimed to trace host-derived macrophages and to evaluate the effects of macrophage infiltration at the recipient site during the early stage on long-term fat graft retention. In our novel mouse model, all mice underwent simulated liposuction and were divided into 2 groups. The fat procurement plus grafting (Pro-Grafting) group was engrafted with prepared fat (0.3 ml). The pro-Grafting+M2 group was engrafted with prepared fat (0.3 ml) mixed with 1.0 × 106 GFP+M0 macrophages, and then, 2 ng IL-4 was injected into the grafts on Day 3. In addition, 1.0 × 106 GFP+M0 macrophages were injected into the tail vein for tracing in the Pro-Grafting group. As a result, GFP+macrophages first infiltrated the donor site and subsequently infiltrated the recipient site in the Pro-Grafting group. The long-term retention rate was higher in the Pro-Grafting+M2 group (52% ± 6.5%) than in the Pro-Grafting group (40% ± 3.5%). CD34+ and CD31+ areas were observed earlier, and expression of the adipogenic proteins PPAR-γ, C/EBP and AP2 was higher in the Pro-Grafting+M2 group than in the Pro-Grafting group. The host macrophages preferentially infiltrate the donor site, and then, infiltrate the recipient site after fat grafting. At the early stage, an increase in macrophages at the recipient site may promote vascularization and regeneration, and thereby improve the fat graft retention rate.

Density-Based High-Quality Fat: Characterization and Correlation with Different Body Fat Ratio.

BACKGROUND: Lipoaspirate can be divided into high-quality fat and low-quality fat using Coleman's centrifugation by adding 0.935 g/ml marker float; the ratio obtained by different individuals is different. OBJECTIVES: This study aimed to examine the HQF obtained from different individuals and establish the relationship between individual body data and HQF. METHODS: We used Coleman's centrifugation method (1200 g, 3 min) with 0.935 g/ml density float to process lipoaspirate and collect HQF from different individuals for the analysis of fat characteristics and in vivo grafting. RESULTS: The HQF obtained from different individuals had similar stromal vascular fraction cell numbers and extracellular matrix content. In animal experiments at different time points (especially 12 weeks), the appearance, retention rate, hematoxylin and eosin staining, and immunohistochemistry results of HQF grafts were similar, while being different from those of Coleman fat. The HQF obtained from individuals with higher body fat ratio was less than those with lower body fat ratio. Following the establishment of the relationship between high-quality fat percentage and the body fat ratio of the donors, we proposed an innovative calculation formula model for the required lipoaspirate. CONCLUSIONS: HQF obtained from different individuals has similar fat characteristics, transplantation process, and outcome. The HQF percentage obtained from different individuals is negatively correlated with the body fat ratio. The amount of liposuction can be predicted using the proposed formula and improve the predictability of fat transplantation. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these evidence-based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

The effects of macrophage-mediated inflammatory response to the donor site on long-term retention of a fat graft in the recipient site in a mice model.

Inflammatory responses mediated by macrophages play a role in tissue repair. However, it is unclear whether the repair in the donor site after liposuction would have any effects on fat graft retention in the recipient site. This study is designed to evaluate the effects of a macrophage-mediated inflammatory response in donor sites on long-term retention of fat grafting. In this study, mice were randomly divided into two groups. One underwent simulated liposuction, called the fat procurement plus grafting (Pro-Grafting) group, and the other underwent sham surgery, called the fat grafting only (Grafting Only) group. The prepared fat (0.3 ml each) was engrafted and cellular events over a 90-day period were assessed. We found macrophages were infiltrated into adipose tissue at the recipient site in the Grafting Only group within 7 days and the repair essentially completed within 30 days. By contrast, few macrophages infiltrated the recipient site in the Pro-Grafting group within 7 days and the entire remodeling process took 30 days longer in the Pro-Grafting than the Grafting Only group. Moreover, C-reactive protein levels were immediately upregulated after surgery, and the inflammatory factors' expression was higher at the donor rather than the recipient site. However, the repair processes and the long-term retention rate became normal when the adipose tissue was grafted after the donor site did not require macrophages for repair. Therefore, we suggest higher inflammatory factors promote macrophage infiltration and the adipose tissue regeneration process at the donor site. This process is delayed at the recipient site, which may affect long-term retention of fat grafts.

Botulinum Toxin A Improves Supramuscular Fat Graft Retention by Enhancing Angiogenesis and Adipogenesis.

BACKGROUND: Autologous fat grafting is commonly used for soft-tissue augmentation and reconstruction in plastic surgery. However, long-term graft retention rates are unpredictable, especially in muscle-related fat grafting. OBJECTIVE: To determine whether botulinum neurotoxin type A (BoNTA) may improve supramuscular fat grafting retention by reducing muscle movement, thereby enhancing angiogenesis and adipogenesis. MATERIALS AND METHODS: Pre-BTX+ nude mice were injected with BoNTA on the right quadriceps femoris and underwent supramuscular fat grafting 1 week later. BTX+ nude mice simultaneously underwent BoNTA injection and transplantation. Control nude mice underwent transplantation without BoNTA. Graft volumes were determined, and grafts underwent histological analyses and immunostaining. CatWalk XT gait analysis was conducted on BTX+ mice. RESULTS: Pre-BTX+ and BTX+ groups had significantly higher retention rates and exhibited better angiogenesis and adipocyte survival than the Control group. CONCLUSION: BoNTA injections improved the long-term retention of supramuscular fat grafts by reducing muscle movement, possibly by augmenting angiogenesis and adipogenesis.

Optimized adipose tissue engineering strategy based on a neo-mechanical processing method.

Decellularized adipose tissue (DAT) represents a promising scaffold for adipose tissue engineering. However, the unique and prolonged lipid removal process required for adipose tissue can damage extracellular matrix (ECM) constituents. Moreover, inadequate vascularization limits the recellularization of DAT in vivo. We proposed a neo-mechanical protocol for rapidly breaking adipocytes and removing lipid content from adipose tissue. The lipid-depleted adipose tissue was then subjected to a fast and mild decellularization to fabricate high-quality DAT (M-DAT). Adipose liquid extract (ALE) derived from this mechanical process was collected and incorporated into M-DAT to further optimize in vivo recellularization. Ordinary DAT was fabricated and served as a control. This developed strategy was evaluated based on decellularization efficiency, ECM quality, and recellularization efficiency. Angiogenic factor components and angiogenic potential of ALE were evaluated in vivo and in vitro. M-DAT achieved the same decellularization efficiency, but exhibited better retention of ECM components and recellularization, compared with those with ordinary DAT. Protein quantification revealed considerable levels of angiogenic factors (basic fibroblast growth factor, epidermal growth factor, transforming growth factor-ß1, and vascular endothelial growth factor) in ALE. ALE promoted tube formation in vitro and induced intense angiogenesis in M-DAT in vivo; furthermore, higher expression of the adipogenic factor PPARγ and greater numbers of adipocytes were evident following ALE treatment, compared with those in the M-DAT group. Mechanical processing of adipose tissue led to the production of high-quality M-DAT and angiogenic factor-enriched ALE. The combination of ALE and M-DAT could be a promising strategy for engineered adipose tissue construction.

Adipose Stromal Vascular Fraction Gel Grafting: A New Method for Tissue Volumization and Rejuvenation.

BACKGROUND: The clinical outcomes of fat grafting vary and are technique-dependent. Stromal vascular fraction (SVF) gel is a novel, mechanically processed fat product with high concentrations of adipose tissue-derived stem cells and other SVF cells. This study evaluated the volumization and rejuvenation effects of SVF-gel. OBJECTIVE: This study evaluated the volumization and rejuvenation effects of SVF-gel. METHODS: This retrospective, single-center study included 126 patients who underwent SVF-gel grafting and 78 who underwent conventional lipoinjection for various indications from March 2015 to February 2017. Patient satisfaction and secondary surgery rates were evaluated. Samples of transferred SVF-gel were harvested and examined histologically. RESULTS: All patients showed improvements in facial augmentation and contour. Patients in the SVF-gel group experienced mild postoperative swelling and a low secondary surgery rate (10.9%). Assessment of patient-rated satisfaction on a 5-point Likert scale found that 77.3% of patients in the SVF-gel group were satisfied (54.5%) or very satisfied (22.8%) with their outcomes. By comparison, 53.8% of patients who underwent conventional lipoinjection were satisfied (48.7%) or very satisfied (5.1%). Moreover, SVF-gel showed effective antiwrinkle and skin rejuvenation effects. Hematoxylin-eosin staining showed a normal adipose tissue structure in transferred SVF-gel. CONCLUSION: Stromal vascular fraction gel is effective for both volumization and rejuvenation, and may be superior to conventional lipoinjection for facial recontouring.

Extracellular matrix/stromal vascular fraction gel conditioned medium accelerates wound healing in a murine model.

Conditioned medium (CM) is a new treatment modality in regenerative medicine and has shown a successful outcome in wound healing. We recently introduced extracellular matrix/stromal vascular fraction gel (ECM/SVF-gel), an adipose-derived stem cell and adipose native extracellular matrix-enriched product for cytotherapy. This study aimed to evaluate the effect of CM from ECM/SVF-gel (Gel-CM) on wound healing compared with the conventional CM from adipose tissue (Adi-CM) and stem cell (SVF-CM). In vitro wound healing effect of three CMs on keratinocytes and fibroblasts was evaluated in terms of proliferation property, migratory property, and extracellular matrix production. In vivo, two full-thickness wounds were created on the back of each mice. The wounds were randomly divided to receive Gel-CM, Adi-CM, SVF-CM, and PBS injection. Histologic observations and collagen content of wound skin were made. Growth factors concentration in three CMs was further quantified. In vitro, Gel-CM promoted the proliferation and migration of keratinocytes and fibroblasts and enhanced collagen I synthesis in fibroblasts compared to Adi-CM and SVF-CM. In vivo, wound closure was faster, and dermal and epidermal regeneration was improved in the Gel-CM-treated mice compared to that in Adi-CM and SVF-CM-treated mice. Moreover, The growth factors concentration (i.e., vascular endothelial growth factor, basic fibroblast growth factor, hepatocyte growth factor, and transforming growth factor-ß) in Gel-CM were significantly higher than those in Adi-CM and SVF-CM. Gel-CM generated under serum free conditions significantly enhanced wound healing effect compared to Adi-CM and SVF-CM by accelerating cell proliferation, migration, and production of ECM. This improved trophic effect may be attributed to the higher growth factors concentration in Gel-CM. Gel-CM shows potential as a novel and promising alternative to skin wound healing treatment. But limitations include the safety and immunogenicity studies of Gel-CM still remain to be clearly clarified and more data on mechanism study are needed.

The Fate of Fat Grafts in Different Recipient Areas: Subcutaneous Plane, Fat Pad, and Muscle.

BACKGROUND: Although fat is transplanted into several layers, including subcutaneous, fat, and muscle layers, there is little (clinical) scientific basis for these procedures. OBJECTIVE: To determine the optimal recipient layer for fat transplantation. MATERIALS AND METHODS: Fat harvested from inguinal fat pads of green fluorescent protein (GFP) mice was grafted into the subcutaneous and intramuscular planes and the fat pads of C57 mice. Specimens collected after 1, 4, 8, 12, and 16 weeks were stained with hematoxylin and eosin to determine angiogenesis and fibrosis in the grafts. The survival rate of donor adipose tissue was determined by measuring GFP expression. RESULTS: Fat was retained longer in fat pads than in subcutaneous layers of recipient mice and longer in subcutaneous than in intramuscular layers. Angiogenesis and vascularized connective tissue were greater in intramuscular than in subcutaneous or fat grafts. Neovascularization, however, was similar in fat pads and subcutaneous grafts. Survival rate was higher for intramuscularly injected fat than subcutaneously and fat pad injected fat. CONCLUSION: Fat pad injection showed the highest graft retention rate, indicating that fat pads maybe the optimal area for fat transplantation. The increased blood supply to muscle suggests that intramuscular injection maybe optimal when there is little movement.

Self-synthesized extracellular matrix contributes to mature adipose tissue regeneration in a tissue engineering chamber.

The development of an engineered adipose tissue substitute capable of supporting reliable, predictable, and complete fat tissue regeneration would be of value in plastic and reconstructive surgery. For adipogenesis, a tissue engineering chamber provides an optimized microenvironment that is both efficacious and reproducible; however, for reasons that remain unclear, tissues regenerated in a tissue engineering chamber consist mostly of connective rather than adipose tissue. Here, we describe a chamber-based system for improving the yield of mature adipose tissue and discuss the potential mechanism of adipogenesis in tissue-chamber models. Adipose tissue flaps with independent vascular pedicles placed in chambers were implanted into rabbits. Adipose volume increased significantly during the observation period (week 1, 2, 3, 4, 16). Histomorphometry revealed mature adipose tissue with signs of adipose tissue remolding. The induced engineered constructs showed high-level expression of adipogenic (peroxisome proliferator-activated receptor γ), chemotactic (stromal cell-derived factor 1a), and inflammatory (interleukin 1 and 6) genes. In our system, the extracellular matrix may have served as a scaffold for cell migration and proliferation, allowing mature adipose tissue to be obtained in a chamber microenvironment without the need for an exogenous scaffold. Our results provide new insights into key elements involved in the early development of adipose tissue regeneration.

Epigenetic regulation of lncRNA connects ubiquitin-proteasome system with infection-inflammation in preterm births and preterm premature rupture of membranes.

BACKGROUND: Preterm premature rupture of membranes (PPROM) is responsible for one third of all preterm births (PTBs). We have recently demonstrated that long noncoding RNAs (lncRNAs) are differentially expressed in human placentas derived from PPROM, PTB, premature rupture of the membranes (PROM), and full-term birth (FTB), and determined the major biological pathways involved in PPROM. METHODS: Here, we further investigated the relationship of lncRNAs, which are differentially expressed in spontaneous PTB (sPTB) and PPROM placentas and are found to overlap a coding locus, with the differential expression of transcribed mRNAs at the same locus. Ten lncRNAs (five up-regulated and five down-regulated) and the lncRNA-associated 10 mRNAs (six up- and four down-regulated), which were identified by microarray in comparing PPROM vs. sPTB, were then validated by real-time quantitative PCR. RESULTS: A total of 62 (38 up- and 24 down-regulated) and 1,923 (790 up- and 1,133 down-regulated) lncRNAs were identified from placentas of premature labor (sPTB + PPROM), as compared to those from full-term labor (FTB + PROM) and from premature rupture of membranes (PPROM + PROM), as compared to those from non-rupture of membranes (sPTB + FTB), respectively. We found that a correlation existed between differentially expressed lncRNAs and their associated mRNAs, which could be grouped into four categories based on the gene strand (sense or antisense) of lncRNA and its paired transcript. These findings suggest that lncRNA regulates mRNA transcription through differential mechanisms. Differential expression of the transcripts PPP2R5C, STAM, TACC2, EML4, PAM, PDE4B, STAM, PPP2R5C, PDE4B, and EGFR indicated a co-expression among these mRNAs, which are involved in the ubiquitine-proteasome system (UPS), in addition to signaling transduction and beta adrenergic signaling, suggesting that imbalanced regulation of UPS may present an additional mechanism underlying the premature rupture of membrane in PPROM. CONCLUSION: Differentially expressed lncRNAs that were identified from the human placentas of sPTB and PPROM may regulate their associated mRNAs through differential mechanisms and connect the ubiquitin-proteasome system with infection-inflammation pathways. Although the detailed mechanisms by which lncRNAs regulate their associated mRNAs in sPTB and PPROM are yet to be clarified, our findings open a new approach to explore the pathogenesis of sPTB and PPROM.

Strategies for Constructing Tissue-Engineered Fat for Soft Tissue Regeneration.

BACKGROUND: Repairing soft tissue defects caused by inflammation, tumors, and trauma remains a major challenge for surgeons. Adipose tissue engineering (ATE) provides a promising way to solve this problem. METHODS: This review summarizes the current ATE strategies for soft tissue reconstruction, and introduces potential construction methods for ATE. RESULTS: Scaffold-based and scaffold-free strategies are the two main approaches in ATE. Although several of these methods have been effective clinically, both scaffold-based and scaffold-free strategies have limitations. The third strategy is a synergistic tissue engineering strategy and combines the advantages of scaffold-based and scaffold-free strategies. CONCLUSION: Personalized construction, stable survival of reconstructed tissues and functional recovery of organs are future goals of building tissue-engineered fat for ATE.

Adipose-derived stem cells in immune-related skin disease: a review of current research and underlying mechanisms.

Adipose-derived stem cells (ASCs) are a critical adult stem cell subpopulation and are widely utilized in the fields of regenerative medicine and stem cell research due to their abundance, ease of harvest, and low immunogenicity. ASCs, which are homologous with skin by nature, can treat immune-related skin diseases by promoting skin regeneration and conferring immunosuppressive effects, with the latter being the most important therapeutic mechanism. ASCs regulate the immune response by direct cell-cell communication with immune cells, such as T cells, macrophages, and B cells. In addition to cell-cell interactions, ASCs modulate the immune response indirectly by secreting cytokines, interleukins, growth factors, and extracellular vesicles. The immunomodulatory effects of ASCs have been exploited to treat many immune-related skin diseases with good therapeutic outcomes. This article reviews the mechanisms underlying the immunomodulatory effects of ASCs, as well as progress in research on immune-related skin diseases.

Adipose Component Transplantation: An Advanced Fat-Grafting Strategy for Facial Rejuvenation.

BACKGROUND: Autologous fat grafting is frequently used for volume augmentation and tissue regeneration. The uniform physical and biological characteristics of fat grafts, however, limit their optimal effects in various situations. Subjecting fat tissue to different mechanical processes results in adipose-derived products with distinct biological components and physical features. The present study describes a novel facial fat-grafting strategy, adipose component transplantation (ACT), that yields different adipose products that can be applied to specific injection sites. METHODS: All patients who underwent ACT were evaluated retrospectively. Fat tissue samples were fractionated into high-density fat, adipose matrix complex, stromal vascular fraction gel, and adipose collagen fragment, as described. Each of these fractions was processed and injected into indicated recipient sites. Additional SVF gel was cryopreserved and, if necessary, injected during the following 3 months. Patients were followed up after 1, 2, 3, and 6 months, and annually thereafter. RESULTS: From March of 2020 to September of 2021, 78 patients underwent whole face fat grafting using the ACT strategy. All operations and secondary injections of cryopreserved SVF gel were uneventful. There were no major complications, and final aesthetic results were satisfactory in 91% of patients. CONCLUSIONS: The ACT strategy allows specific adipose products to be applied to specific injection sites, as warranted. Adipose matrix complex is indicated for sufficient rigid support, high-density fat when large volumes are required, SVF gel for precise injection and cryopreservation, and ACF as mesotherapy for skin rejuvenation. The ACT strategy optimizes the biological functions and physical features of different adipose-derived products. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.

Attenuated angiogenesis and macrophage infiltration during adipose tissue regeneration in a megavolume human fat grafting nude mouse model.

BACKGROUND: Survival and regeneration mechanisms of large (>250 mL) fat grafts remain incompletely understood. In fat grafts from volunteers with megavolume fat transfer breast augmentation, neovascularization and inflammatory cell infiltration decreased within 7 days according to histological analysis. We further investigated this phenomenon using a nude mouse model. METHODS: To simulate clinical contexts, chambers containing 1 mL human fat were implanted into nude mice. Chambers allowed selective transfer of tissue fluid from recipient nude mice into chambers, but not capillaries or macrophages. Seven days later, fat was removed from the chamber and reimplanted into a new nude mouse in the open-chambered fat group (OCFG, n=45). Adipose samples from volunteers and explanted grafts from OCFG were subjected to histological analyses. Graft weight, vascularization, and immune response were also compared between the OCFG and conventional direct fat grafting (control group (CG)). RESULTS: Percent tissue integrity, percent fibrosis, adipocyte viability, and neovascularization did not significantly differ between volunteer samples and OCFG grafts at day 7. On day 90, OCFG retention rate was decreased relative to CG and the fibrosis area was larger in the OCFG than in the CG. However, the macrophage and capillary counts were lower in the OCFG group relative to CG at days 7 and 14 after transplantation. CONCLUSIONS: The present study provides histological analyses of megavolume fat grafts sampled from clinical breast augmentation tissues and a xenograft nude mouse model. However, these preliminary results in a small clinical cohort should be further assessed in large allogeneic animal models.

Stromal vascular fraction (SVF) cells enhance long-term survival of autologous fat grafting through the facilitation of M2 macrophages.

Optimum perfusion may be the key to the endurance, and hence survival, of autologous adipose tissue transportation. Stromal vascular fraction (SVF) cell therapy can greatly improve the survival of fat grafts by enhancing angiogenesis. However, SVF cells are poorly retained in later stages of SVF-assisted adipose tissue transplant. Therefore, it hardly defines the angiogenic effect through long-term transportation. Adipose tissue suffers from acute hypoxia in the early stage of transportation, leading to the recruitment of macrophages. M2 macrophages enhance angiogenesis in adipose transplantation by acting as an angiogenic signal source, promoting tip cell migration and assisting tip cell fusion. Furthermore, the angiogenic and anti-inflammatory micro-environment in the graft created by M2 macrophages may stimulate the transformation of infiltrating macrophages to M2 macrophages. These M2 macrophages may enhance the long-term retention of graft through angiogenesis. Based on these observations, we postulate that the long-term angiogenic effect of SVF cells may be achieved through the facilitation of the M2 macrophages.